ioo PRACTICAL HISTOLOGY. 



under the sarcolemma (Doyere's eminence) ; but it is 

 exceedingly doubtful that this plate is the real termination 

 of the nerve, for, after staining with gold, Gerlach has found 

 a plexus of fine varicose fibrils like nerve fibrils through- 

 out the muscular substance. (Sitzungsberichte der Phys. Med. 

 Soc. ; Erlangen, 1873.) Kiihne's article on this subject in 

 Strieker's Histology, vol. i. p. 202, may be advantageously 

 consulted by the advanced student. 



BLOOD-VESSELS. 



1 6 1. Structure of Blood- Vessels (H.) Blood-vessels 

 may be conveniently prepared from the pia mater ; that of 

 a sheep does perfectly. With scissors remove a slice about 

 a quarter of an inch in depth from the surface of a cerebral 

 convolution. Lay it upon a slide, with the pia mater 

 touching the glass. Fix one side of the slice with forceps, 

 and with the back of a scalpel gently scrape away the brain 

 matter. With a camel-hair brush and water, " pencil" 

 away the remainder. Tease with needles ; cover, and 

 examine in water. 



a. Capillaries. Observe the nuclei in the capillaries. 

 They appear to be placed in a homogeneous membrane, 

 but in a silvered preparation it will be seen that the 

 membrane is mapped out by silver lines into polygonal 

 areas, each one enclosing a nucleus. These are, therefore, 

 the nuclei of epithelial squames, with which the whole 

 vascular system is lined. Whether or not a very delicate 

 homogeneous membrane lies outside the epithelium of the 

 capillary is doubtful. 



If the capillary be traced up to a large vessel, the first 

 obvious change consists in the addition here and there of 

 a non-striped muscular fibre coiled round the vessel ; then 

 the other tissues found in the larger vessels make their 

 appearance. 



b. Small arteries and "veins. In small arteries and 

 veins three coats may in general be recognised. The inner 

 coat consists of an elastic membrane lined by a single layer 

 of squamous epithelium. The middle coat is composed of 



